Conventionally, an optical-sensor-equipped display apparatus has been proposed that is made capable of detecting a brightness of external light and capturing an image of an object approaching its display panel by providing photodetecting elements such as photodiodes. Such an optical-sensor-equipped display apparatus is supposed to be used as a display apparatus for two-way communication, or a display apparatus having a touch panel function.
In the case of a conventional optical-sensor-equipped display apparatus, when known composing elements such as signal lines and scanning lines, TFTs (thin film transistors), and pixel electrodes are formed through semiconductor processing, photodiodes and the like are formed on an active matrix substrate through the same processing (see JP 2006-3857 A, and “A Touch Panel Function Integrated LCD Including LTPS A/D Converter”, T. Nakamura et al., SID 05 DIGEST, pp. 1054-1055, 2005).
Further, it is known that a sensor output largely depends on an ambient temperature in an optical-sensor-equipped display device. In other words, there is a problem that when the ambient temperature varies, the characteristics of photodetecting elements fluctuate with the variation, which results in that variation of a light intensity cannot be detected correctly.
Such a temperature dependence of an optical sensor is ascribed to a dark current (also referred to as a leak current). As a configuration for calibrating a dark current component in an output of an optical sensor, the following configuration is known: on an active matrix substrate, a light-shielded photodetecting element for detecting only a dark current (reference element) as a so-called dummy sensor is provided in addition to a photodetecting element for detecting an intensity of incident light (photodetecting element) (see JP 2007-18458A, JP 2007-81870 A, and “LTPS Ambient Light Sensor with Temperature Compensation”, S. Koide et al., IDW '06 pp. 689-690, 2006). In this conventional configuration, an output from the reference element reflects the dark current component. Therefore, a sensor output with temperature dependence reduced can be obtained by, in a circuit at a later stage of the optical sensor, subtracting an output of the reference element from an output of the photodetecting element.